Introduction

An important issue in converted wave seismic processing is how to deal with the polarity reversal that occurs near zero-offset. Conventional methodology Harrison and Stewart (1993) involves multiplying the data recorded at negative offsets by -1. However, this approach fails where there is structural complexity and non-constant v_p / v_s ratio ($\gamma$).

For P-wave datasets, angle-domain common-image gathers [e.g., Prucha et al. (1999); de Bruin et al. (1991)] decompose reflected seismic energy into components from specific opening angles ($\theta$). Since the PS-wave polarity reversal occurs at normal incidence ($\theta = 0$), the angle-domain common-image gathers provide a natural domain in which to address the polarity reversal problem. Moreover, analyzing angle gathers for converted wave seismic data may lead to: velocity analysis and amplitude versus angle analysis for converted waves.

In this work we present a theoretical discussion of the polarity reversal problem. We image PS-wave data into offset-domain CIGs with a prestack recursive depth migration algorithm. We use the radial-trace transformation introduced by Sava and Fomel (2000) to obtain angle-domain gathers after migration. We reinterpret the opening angle ($\theta$) for the case of converted waves, this leads to a solution of the polarity reversal problem that is valid for any structurally complex media.